Low power circuitry, including amplifiers and buffer amplifiers, find utility in a number of applications, including battery operated equipment and in applications wherein the overall circuit volume must be small.
One particularly useful application for low power circuitry is in providing readout circuits for an array of radiation detectors that are cooled to cryogenic temperatures during operation. The readout circuits are preferably fabricated in integrated circuit form, and typically include analog signal switching elements and amplifiers. In such assemblies it is often desirable to locate the integrated circuit readout at or near to a focal plane array (FPA) of cryogenically cooled radiation detectors, such as those comprised of Group II-VI semiconductor material and optimized for detecting infrared (IR) radiation.
In such applications it is known to hybridize the FPA with the readout integrated circuit through the use of indium bump technology. This serves to minimize the lengths of interconnections between the FPA and the readout circuitry, which in turn reduces parasitic capacitance, reduces electrical noise, and increases the speed of operation.
It can be appreciated that when locating the readout integrated circuit at or near the cryogenically cooled focal plane, it is important to minimize the operating power consumption of the readout integrated circuit to avoid placing a large heat load removal requirement on the cryogenic cooler assembly. Another important aspect of power reduction is to reduce as much as possible a quiescent power consumption of the circuitry.
Another important consideration is to provide readout circuitry that is amenable to a simplified construction. This tends to increase the density with which such circuits can be integrated upon a common substrate, and furthermore tends to increase the overall reliability of the FPA/readout assembly.
A conventional circuit for providing isolation between two stages of circuitry is the source follower. However, the conventional source follower does not provide gain and, in fact, typically introduces an undesired attenuation to a signal propagating between two stages of circuitry. That is, the conventional source follower is not a true unity gain circuit. The conventional source follower also requires a current source for operation (thereby consuming significant power even in a quiescent state), and has a slew-limited response speed that is, in part, determined by the required current source.
Buffer stages have also been constructed using operational amplifiers in a closed loop configuration. While these circuits exhibit good drive capability, they are generally complex and require relatively higher power to operate than the conventional source follower.
It is thus an object of this invention to provide a low power amplifier circuit that overcomes the problems of the prior art.
It is another object of this invention to provide a buffer amplifier circuit suitable for fabrication on an integrated circuit, the buffer amplifier circuit featuring programmable gains that may exceed unity, a negligible quiescent power dissipation, and an improved response speed over conventional circuitry.